Above all else: do NOT use an all-purpose detergent, fabric softener or bleaching agent on your rain jacket. Furthermore, liquid detergents are more suitable than powder, as the latter can clog the pores. But please be careful, even with liquid detergents: some liquid detergents contain a fabric softener. Mild detergents or ones especially geared towards outdoor functional clothing are best of all since the detergent washes out easily.
Do not overdo the amount of detergent for washing your rain jacket. In general, it is better to wash often, using a small amount of detergent, than to wash rarely and use a lot of detergent.