I'm relatively new at this keg thing, but didn't see anything similar on this forum. Apologies if this is common knowledge.
I blatantly stole these instructions to build my own little hand pump to clean and sanitize my beer lines:
A plastic garden sprayer, a brass fitting, and a spare Firestone ball lock post, and boom. Works great for me. I pump cleaner through my line, let it sit for fifteen minutes, flush, then pump water through to rinse, then pump StarSan through. Seems easier to me than putting solution in a keg, pressurizing the keg, and pushing it through with co2.