I use the camomile stuff from Pets at Home, it smells nice.
For bathing them I use a washing-up bowl on the kitchen floor, & fill the sink with clean water for rinsing. Fill the bowl with a few cms of warm water, wet their backs using a jug then lather up the shampoo in one hand, I usually restrain the pig with my left hand under her chest, propping her up a bit & lather with the other hand. Lift them out of the water to shampoo the back legs & other bits, then back in the water & rinse them off. Change the water if it's a bit soapy. Then pop them in a towel to absorb most of the wetness, & I usually put a big towel on the sofa & let them wander around a bit - they do like to shake themselves off! They dry off quite quickly & will groom themselves whilst they're drying.