Shower waste, traps and NRV's

[Cordless Crazy]

A few questions:

1. When fitting a chrome shower waste grid with a back nut and two rubber seals, would you use silicone to provide an additional seal to the tray when clamped?

1. Am tiling the floor of my new bathroom, so any access to the trap after the shower tray is installed, will be nigh on impossible. What is the best trap to fit in a situation where I can really never get back to it in a hurry? Anti-vac bottle trap or regular 75mm P trap?

2. Due to the arrangement and levels of the pipes, the shower waste will being connecting in to a horizontal soil pipe on the side. Should I be overly concerned with a possible blockage in the stack and back-flow up the shower waste? Would hate to see parts of Mr Hankey popping up in the shower tray. Is it wise to fit a McAlpine non-return valve? How reliable are these with hair and gunk from a shower?

[Ret.]

When I did a complete bathroom makeover three years ago, I replaced the airing cupboard with a shower cubicle and connected the drain from the shower into the same pipe that the sink and bath drain into prior to reaching the soil stack.

Of course I should have foreseen that when the bath was emptying the water would back up and start to fill the shower tray! Fortunately for me I had had no choice but to fit a raised shower tray and so I was able to remove the trim below the tray and get in to fit a horizontal hepvo valve just after the normal shallow shower trap. It has worked fine since fitted and has not clogged up or required cleaning.

[Skipweasel]

Would I be right in thinking you don't share a house with three long- haired individuals?