The old waste pipe, which goes through the outside wall, is higher than sloped waste from the bath. The plumber decided to elbow this up. He said this wouldn't be a problem as the water would push the waste water through, but the sloping part would always contain water.
The problem we have is the drainage from the bath isn't very quick. Having a shower can cause water to remain in the bath before slowly draining away.
I've read about these hepVo traps being used in places where space is tight. Would this help with our slow drainage problems if I elbowed straight from the waste of the bath to the hepVo then slope to the outgoing pipe?