We've recently had a new bath installed (& turned around), due to the
way the waste is located the plumber installed a shallow waste trap
(which is cut into the floor) followed by a series of slightly sloping
bends before it reaches the old pipe which connects to the outside
main waste down pipe.

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?

TIA

Dave