Waste disposal points in Wales

hi,

I am thinking to take a trip to Wales (Brecon Beacons and then Pembrokeshire) in the coming weeks and wondered if anyone knows of any club sites, or other parks where you could pay to dispose of grey and black wastes after a few days of 'wild camping'. I will be staying at a couple of club sites also but there will be some days where i'm not and so any info on potential places who offer this service would be most appreciated!

Thanks in advance