Admittedly it's a bit weird sitting on a plastic box in a van the first time you do it, but once you've been away with a porta-potti in the van you'll realise how useful it is. My wife hated the idea of it, but once she actually needed to use it she was converted, and now wouldn't be without.
A few things from our experience:
- The thetford ones are loads better than the others. They're made of a different, more rigid plastic which is easier to clean, have a level gauge, an emptying spout and flush better. Otherwise just buy the cheapest one - all the cheap ones are pretty similar.
- The blue chemical stuff stinks; I can't bear it. We used to use the green stuff, but now use Asda smartprice bio washing liquid, which seems to work just as well and leaves the holding tank lovely and clean
- No need for any of the pink stuff in the flush tank really. We stopped using it a few years ago with no apparent difference
- On the face of it a bigger one seems to be a good idea, and they're certainly a bit more comfy. But you'll want to empty it pretty regularly, so if cupboard space is at a premium, get a little one
Thetford type:
THETFORD PORTA POTTI QUBE 365 TOILET WITH FREE AQUA KEM AND AQUA RINSE 92817 | eBay - there are small ones too which are a bit cheaper.
Cheap one:
NEW PALM SPRINGS 10 LITRE PORTABLE TOILET FOR CAMPING | eBay - if you look around you can get these for about £25.
Don't be tempted by the 'bucket' type, e.g. Kampa Khazi - you'll have to empty it before moving or it runs the risk of spilling. The porta potti type is sealed so is fine to drive with. Oh, and don't buy the special toilet paper, it's useless. Lidl cheapest stuff is ideal, because it breaks up with the swishing around...