There should be a seal at the tank entrance on top of tank that should be tight.
Had a 3" PIPE fall out of floor flange for toilet into the black tank and slipping out of floor flange because it was never glued and crated a mess one day when traveling.
When I re-lifted the 3" pipe up to glue back into the floor flange the collar around pipe was tight but with pulling pressure and twisting was able to gain the pipe necessary to glue back in floor flange.
Would think the vent pipe would have same collar.
Go into COM_NET
---- Catalog Model Year --- 2005 ---- 2005 KSCA ---- Adhesives & Sealants ----- Sealant & Gaskets, will give you the lists of various sealants used in your coach.
Use the top heading or you will get the Brochure for coach.