ProDave

If that is ALL the insulation you are fitting on a (assumed) un insulated floor, then the electric UFH will be very ineffective and very expensive to heat as a huge proportion of the electricity used will just be heating the under floor space. Most people consider a minimum of 100mm thick PIR type insulation to be required. And in any event electric UFH is probably the most expensive way to heat a room, and no means to repair a fault in the heating mat if one occurs.

At probably £200 per pump out, it would soon be cheaper to do it properly.

Hi and welcome, you are in good company.

Looks like the cheap gold plating has failed. Wrap the replacement in self amalgamating tape, and honestly a bit of vaseline smeared on the connector pins before engaging keeps water out. (I do this on boat connections)

Just watched it, (rarely watch commercial television live) Under budget, under time and no major problems. Kevin was having to dig deep to find any tiny little problem to highlight no matter how small. A model of just how to do a self build, and a great result. Of course it only went so well because of all the expert advice and encouragement from Buildhub.

This seems popular according to google https://www.diy.com/departments/nature-calls-composting-toilet/5060542053747_BQ.prd

Why not build or buy a composing toilet so it is only grey waste water you have to deal with?

This is the sort of thing most touring caravans use to collect their grey waste water and wheel it to the appropriate drain on a site.

This is the Marsh portable treatment plant designed to slide under a static caravan. It will discharge grey waste water that still needs to go to a soakaway or possibly to a watercourse. https://www.theseptictankstore.co.uk/shop/marsh-portapura-m5-sewage-treatment-plant-5-person/#:~:text=Description,also perfect for glamping accommodation.

That is an "aquaroll" other makes are available) for transporting fresh drinking water to a touring caravan. Nothing to to with waste.

Marsh make a small "portable" treatment plant designed to slide under a caravan.

He is making it into a "high integrity" CU with as you describe one way not protected by either RCD which is okay for the SWA. He needs to have the appropriate extra cables inside the CU. Some will argue if it is not supplied like that by the manufacturer then it is no good.

Buy a decent amount of Kwikstage or similar system scaffold and do it yourself. It will easily sell at the end of your build, but I kept some of mine, enough to scaffold 1 wall of the house.

IF you want maximum yield. But if self using and not getting paid for any export there is a big argument for a much steeper pitch, even near vertical, to get more production in winter at the expense of less than optimal production in summer, but you usually generate more than you can use in summer anyway.

It would not be my choice, neither would those plastic pipe fittings be. What did you agree with him before hand?