McAlpine VP3 Air Admittance Valve

[screamer]

My shower waste (all pipework is in the garage below at ceiling height) is on a pretty long run, nearer the stack the bath Tees into it waste, when the bath drains I get the suction going to the shower trap.
Can I fit one of these in-between the shower & bath wastes or do these need to be above water line/flow?

 

[screamer]

Can I fit this straight off of my bath trap? (McAlpine HC2650UK)

 

[Scally-Ho]

There is no good reason why that air admittance valve can't be fitted straight after the bath trap, but I would have gone for an anti vac trap.

 

[screamer]

I was seeing the 50mm bath traps with the anti syphon on them so thought of the standalone version.
The bath waste I have includeds the trap and the fitting comes off level with the floor.

I do plan on separating the bath waste after I start on the toilet, instead of a 90deg bend going up to the toilet I'll fit a tee then a cap end with waste opening for the bath.

 

[Scally-Ho]

Your shower waste should ideally be separate from the bath and/or basin wastes.

 

[Madrab]

Unfortunately your installer didn't considered that when the waste run was installed, never the best to put a bath and a shower on the same run.
That's an inline anti vac valve, so doesn't really need to be above the highest spillover, best practice though is it should be as high as possible though just in case. Trouble is they should really be in a spot where they can be serviced as they can need periodical cleaning, especially when/if they stick open.

The other option would be to fit an anti vac bath trap but it does need extra installation height.