My garden has very poor drainage due to clay under the soil, i've read that i have to dig a soak away or drainage channels. But exactly how do i do this and what sizes should they be etc??
Not something to be rushed. No point in digging soakaway, channels etc if the soil is so clay based that the water wont soakaway anyway. Firstly, try a few small test holes down 2 or 3 feet (best done in the winter) if they fill with water, then a soakaway wont work. A sump and a pump may be the alternative if it is a real problem.