Garp wrote:
MEK stands for Methyl Ethyl Ketone. More commonly known as solvent
cement/glue for solvent pipe fittings.
It doesn't tend to work on most plastics other than water pipe.
It's a solvent mixed with plastic powder to make it thick and gooey - by
itself it's like water and very runny, so they add plastic powder to make it
easier to work with and to give it some density.
It works by melting the plastic of the item it is applied to (plastic water
pipes being the favourite). Painted on the ends of the 2 pipes, they go
sticky, plug em together and the whole lot sets usually in a couple of
minutes.

I'm not sure about a shower tray, as the strength of MEK relies on
overlapping surfaces melting and bonding together. The shower tray won't
have this overlap.

No, MEK will glue styrene end to end as used for plastic model kits. No
need for an overlap.

MBQ