Old Techo wrote:Justin, all I am saying is you do not need to have waste pipes of that capacity in a caravan.
In a van the water flows both in and out are less than in a regular house kitchen. Once upon a time waste pipes were 2 inches or 50 mm. The rules changed before I installed my spa about 10 years ago and 40 mm was deemed enough. So here is my spa with a legal 40 mm drain and able to happily cope with emptying 300 litres.
When you are free camping water can be so precious you will be happy for waste to discharge through a drinking straw
the reason that Baths, including spas, changed to 40mm outlets was because we started connecting them to floor-waste gullies. Don't want to flood the floor-waste gullies, do we???.
Now to that much admired "S" trap.
Personally, I would lose it and replace it with a "HEPVO" valve and definitely install one on the low fixtures (shower) as they also act as a reflux valve. Don't want the sink filling the shower.
If the outlet hose doesn't have continuous fall there is a real risk of having an air-lock at the "S" trap and the sink may refuse to drain.
And finally, unless you have an open 50mm end to drain the solids will stay in the trap and be a PITA.