As Kate and co say - you could start at the bargain end with a bucket and lid ( £5 from Mothercare, a splash of Zooflora, weewees only, chuck it down the chemical disposal point in the morning) That has done us fine for years.
Porta potti type things have never appealed to me because of the extra bulk of packing it and all the faffing about with different chemicals.
The only kind of camping loo I would consider would be the PETT system - a sturdy loo which works with a plastic bag full of gelling/deodorising powder which renders ALL bodily waste harmless so you can just throw the sealed bag into normal bins. But it aint cheap for the full kits, so some folks on here just buy the special bags (WAG bags) and powder (POOH powder - stupid names but then it IS American in origin!) There is a previous thread about them here
There is a UK supplier here complete with demo video - happy watching!
We have a posh bucket cos its got a toilet seat and a lid to carry it to the elsan point. Like Foggers and family its only for weewees and we prefer Zoflora to the Elsan Blu which is a bit overpowering in a bucket rather than the cassette. I have seen something similar to ours on ebay (new not used) for about a tenner.
bucket and chuck it`s the norm, also you could use amongst other chemicals, a splash of savalon disifectent, like the others have said its for water waste only unless desprate.
any baby outlet sel nappy buckets with lids for a fiver and they are strong enough to take the weight of a adult.
not worth the extra of of packing a pp for a w/e and dont forget in a tent you cast a nice Silhouette if you not in the bedroom and light is on, the no seeum mesh is the bedrooms not the main fly, you would need a outside toilet tent and pp if you go for longer stays, or tie a not in it, cross legs dont drink after nine.
We've got the bucket with lid, you dont use bags just the disinfectent, then take it to the chemical disposal point in the morning like the others have said, but what I like about the bucket is the fire bucket fits inside and then our 907 camping gas cylinder inside that, so no wasted space in the car.
I do like the look of the pet system and have tried the wag bags which were very good, but the bucket is a lot cheaper, so will just use the wag bags when there are no facilities on site.
We always take the Porta Potti no matter what. But this is only because we have one and my OH is quite fussy when it comes to toiletting. Its not easy explaining to her that a Porta Potti is just a bucket thats moulded to look a bit more stylish so I just take it for an easy life.