Thor Forums

[Judge]

I've had a couple Thor motorhomes and the bathroom sink is plumbed into the Black Tank. There are many theories as why this is the case...

- Helps to keep more water in the black tank for more efficient dumping
- To reduce the amount of water going into the grey tank
- Easier plumbing


As previously mentioned... if you were hooked to the San-T-Flush port and not the fresh water fill that would cause the problem.

Just looking at how these rigs are plumbed, I can't see how filling the fresh water tank could get water into the black tank.

When the fresh water tank is full, there is an overflow at the top of the tank that allows the excess water to come out right next to the fill port. The fresh water tank can't be pressurized from filling such that it could push water past the pump.

Even if the fresh water tank could become pressurized from filling, there would also need to be a serious plumbing problem for fresh water to get into the black tank.

There is a Vacuum Breaker for the San-T-Flush system that prevents the black tank from siphoning back to the San-T-Flush hose port. There have been times when that has failed or was plumbed incorrectly and it typically causes a leak on the coach floor (my two coaches had the Vacuum Breaker behind the shower wall.