good to blow water lines, but if you want to add glycol, crawl under at HWT, there is a sheet metal panel screwed on back. Remove screws and you'll find a 3 way ball valve so you can divert water/glycol from HWT to system. I just MT water tank and put in a 9 liter jug of glycol and pressurize system. Open each tap till you see technicolor of glycol. Add a liter or so at each sink trap. Be sure to get glycol into toilet flush valve., ice maker, and alternate filtered water outlet at kitchen sink.
2000 Bounder. 2000 Vanguard 17' boat, 5 dogs, 2 cats, 1 miniature ponies, 1 horse, Massey MF65, 2013 Kia Sorrento, 2003 GMC Sierra Denali Quad Steer- 1 longtime patient wife(56 yrs)