Suctioning/Pumping out black/grey tanks

[SnowNCycle]

I searched forum and found nothing on this matter, so sorry if a duplication, but I have never had to do this before. I have a 2019 Thor Aria 4000 DP and was at a fair over the weekend with our band which was performing and parked near the stage where there was no sewer hook-up. When our tanks were full, they sent over a pumping truck for us. The guy had the exact standard connection we all use on our RV's and he said he does it all the time, so he connected to the end of my sewer hose and started a pump on his truck. What concerned me was that when the black tank was fully purged, my sewer hose got sucked flat! I quickly closed/opened the black/grey tanks nearly simultaneously, the hose relaxed a bit and the grey tank was then purged. After it was empty, the hose went flat again and the suction continued for a bit until he went back and turned off the pump. My concern was that the suction somehow damaged my tanks or plumbing. Although it sucked my dump hose flat, there was no damage or holes in it. I know both systems have vents and obvious openings at the points where they drain, so I assume the suction is just pulling air through those openings? Are my concerns legitimate or is this practice fully acceptable and harmless?

[TandW]

Originally Posted by SnowNCycle

I searched forum and found nothing on this matter, so sorry if a duplication, but I have never had to do this before. I have a 2019 Thor Aria 4000 DP and was at a fair over the weekend with our band which was performing and parked near the stage where there was no sewer hook-up. When our tanks were full, they sent over a pumping truck for us. The guy had the exact standard connection we all use on our RV's and he said he does it all the time, so he connected to the end of my sewer hose and started a pump on his truck. What concerned me was that when the black tank was fully purged, my sewer hose got sucked flat! I quickly closed/opened the black/grey tanks nearly simultaneously, the hose relaxed a bit and the grey tank was then purged. After it was empty, the hose went flat again and the suction continued for a bit until he went back and turned off the pump. My concern was that the suction somehow damaged my tanks or plumbing. Although it sucked my dump hose flat, there was no damage or holes in it. I know both systems have vents and obvious openings at the points where they drain, so I assume the suction is just pulling air through those openings? Are my concerns legitimate or is this practice fully acceptable and harmless?

Those super-sucker trucks can develop 21 inches of vacuum or more depending on operator settings. They can collapse an empty drum. As you say your hoses were drawn flat I doubt that any appreciable vacuum was affecting your tanks. But had your hoses been stiffer I might be concerned with imploding tanks and vent piping pulling out of them if not the drain piping itself. But, likely the mobile sewer service guy knows what he is doing. Any of your neighbors have the same experience?

[Lt Dan]

It's a common practice to vacuum out the tanks like that. More than likely the pump was pulling more air than what the vent pipe could supply once the contents were drained causing the hose to collapse.

[Ohio44718]

I can understand your concerns. The sewer hoses are pretty flexible, but surprised that there was enough suction to draw it flat unless both gate valves were closed. When I had my tanks pumped in Sturgis, they did not use my hoses at all thus did not see anything like that. I would think a good chance the water in the traps got pulled out. No big deal just run a little water in each area. My other concern would be the air admittance valves on the drain lines. If you start getting any odor in the coach, that would be my first place to investigate.

[MrMark52]

As with any sewer system, gray and black tanks should be vented to the roof of the coach. This allows the air in the tank to be displaced by the water coming into the tank. Otherwise your toilet will burb at you when you flush it, or your sinks won’t drain properly. It would be very odoriferous inside the coach.

If the vent to the tanks are plugged, air cannot be drawn back into the tanks to replace the “fluid” being sucked out by the honey truck.
Yes, honey truck vacuum systems can reach 21” of mercury vacuum, but the volumetric flow rate is not real high at that vacuum. A quick check of a few sewage vacuum pumps shows ~127CFM to ~250CFM. But keep in mind, if there isn’t enough liquid flow in the hose, then the vacuum pump will try to draw air assuming it can get the air from the tank as described above.

Not to forget RV sewer hoses aren’t made for vacuum service, even though if the system is properly vented, little if any vacuum should occur in the hose.

You need to make sure all your roof vents are clear. Mud daubers like to build nests in them, as do birds and other critters of our environment.
Some coaches have vents in the cabinets under the sink, although they are usually not the primary means of venting the tanks. Those vents need to be confirmed to be working (they are basically a check valve, allowing air to escape when fluid is flowing into them but sealing to prevent the release of odors at other times).

[shootist]

No way the roof vent can supply the amount of air needed. If there is a next time hold the toilet lever open, for the black and stand ready to shut the valves off as soon as you see the hose start to collapse. You don't know what the long term effects on the tanks and fittings will be, and maybe neither does that driver.

[Old-Biscuit]

NEXT time TELL the Operator to NOT pull anymore vacuum then 10" (just slightly above idle on the vacuum pump)

A Vacuum/Septic truck CAN Collapse your Waste tanks

Sewer hose would NOT have collapsed IF guy knew what he was doing
1 1/2" Vent line vs 3" dump line and high vacuum sucking....recipe for disaster
Waste tank is gravity feeding so very little vacuum is needed

Did this guy damage yours...........you'll know when you fill them up
WATCH for any Leakage

[Mudfrog]

Originally Posted by shootist

No way the roof vent can supply the amount of air needed. If there is a next time hold the toilet lever open, for the black and stand ready to shut the valves off as soon as you see the hose start to collapse. You don't know what the long term effects on the tanks and fittings will be, and maybe neither does that driver.

I never had an inkling the vents weren't big enough to handle a pump out. I know I'll watch very carefully if I ever have to resort to using that service.

Originally Posted by Old-Biscuit

NEXT time TELL the Operator to NOT pull anymore vacuum then 10"

A Vacuum/Septic truck CAN Collapse your Waste tanks

Did this guy damage yours...........you'll know when you fill them up
WATCH for any Leakage

For sure, I'd definitely ask that his pump be dialed down if possible. No matter the setting, the pump operator should have stopped pumping at the first sign of the collapse.

[TandW]

Originally Posted by Mudfrog

I never had an inkling the vents weren't big enough to handle a pump out. I know I'll watch very carefully if I ever have to resort to using that service.



For sure, I'd definitely ask that his pump be dialed down if possible. No matter the setting, the pump operator should have stopped pumping at the first sign of the collapse.

The thing is, the operator needs to draw air so that he can slurp up every last drop without leaving behind a mess.

[Old-Biscuit]

Originally Posted by TandW

The thing is, the operator needs to draw air so that he can slurp up every last drop without leaving behind a mess.

That doesn't require collapsing the sewer hose
Vacuum pump at idle will handle it just fine

[TandW]

Originally Posted by Old-Biscuit

That doesn't require collapsing the sewer hose
Vacuum pump at idle will handle it just fine

Agreed. But this was a situation with a collapsed hose, thus no air flow.

[Old-Biscuit]

Originally Posted by TandW

Agreed. But this was a situation with a collapsed hose, thus no air flow.

Because vacuum was too HIGH...3" sucking vs 1 1/2" air venting

Popcorn Emoji suggests 'sitting back to watch the fur fly'....over used

[TandW]

Originally Posted by Old-Biscuit

Because vacuum was too HIGH...3" sucking vs 1 1/2" air venting

Popcorn Emoji suggests 'sitting back to watch the fur fly'....over used

Agreed. On both counts.

[johnhicks]

We had poopie-man service for a year. He told us that the company had been stuck paying for collapsed rv tanks a few times. The way he did it was that he stuck his pipe downward into the end of our hose, which was tilted upwards. He started the suction and we opened the valve; he could slurp it all up without collapsing anything.

Another poopie man brought a bucket; we drained into the bucket and he slurped out of the bucket. Then we ran a little water to rinse his bucket.