contaminating

[Brownlie]

Maybe you can find some synonyms for piss. This poem seems rife with undercurrents that I think can be drawn out. I don't think the subject of the poem is drawn out enough. I hope you edit this poem more to see what it can turn into.

I pissed in the bathwater, -- When did you piss in bathwater? Who is this narrator is he young or old?
lay back and opened up the bladder valve.
It's a great feeling unleashing; -- It is a great feeling especially after you've had to hold it in for a long time.
the gush of a full tank,
but there was no profundity.-- Why was there no profundity?I've pissed in cold swimming pools - Maybe you could describe the incident where the narrator pissed in the swimming pool. What was the water like?
there was purpose, a sense of achievement --Why did that cause a sense of achievement
a young lad astride his stallion.

"look at me pissing, yes pissing"

In your swimming pool. -Bastard!

Warm piss cupping cold balls like matron
on scabies inspection in the kids home. -- You could write a whole poem about a matron inspecting scabies. I would be very interested to read about that.
Turned out she liked inspecting balls -- I get the feeling this is alluding to something dark it could be my imagination. If it's not I like dark
as much as I like pool pissing

I learned that piss in bathwater doesn't make soap
lather yellowed or smelly, pissy smelly,
not fragrant smelly like matron is when you rest
your hands on her stout shoulders -This is a good line
and cough as she says

"cough,"

and sighs.

I remember the ammoniac smell of piss
stained sheets piled on bare floorboards, -- I really like these first two lines in this stanza, but you may want to get rid of the word piss here unless you are talking about wetting the bed. "Bare Floorboards." seems evocative.
a mountain of light brown and crisp white.
A mountain of piss. -- You repeat a lot of words sometimes that works but you could try using new words just to see what you can come up with.

This poem seems fragmented as it sits, but I think it would be fruitful for you to edit this poem and draw out some details and fully explain some of the things you're trying to describe. I tried my best with your poem, hopefully my comments weren't too far off the mark. Everybody on the site should comment on this poem, because you always do your part.