If you drain something, you remove the liquid from it, usually by pouring it away or allowing it to flow away, and if something drains, liquid flows away or out of it:
Kitchen and bathroom sink drains can trap food and bacteria that cause smelly odors. Learn how to clean a sink drain using baking soda and vinegar (no chemicals!) so it smells fresh and drains well.
Drain definition: to withdraw or draw off (a liquid) gradually; remove slowly or by degrees, as by filtration.. See examples of DRAIN used in a sentence.
drain /dreɪn/ v. to empty by drawing off liquid: [~ + object] to drain a swamp. [~ + object (+ of + object)] Drain the wound (of blood) before you apply the bandage. [no object] The crankcase has to drain before you put on the new filter.
Look up drain in Wiktionary, the free dictionary.