Depending on the type of airplane, if it is a cowled (scale) engine installation, to avoid the mess inside and to avoid oil dripping all over the house when moving or storing the airplane, insert a piece of large silicone fuel tubing, going from the crankcase nipple to a piece of brass tubing, which can be attached (strap and screws) to the firewall and protruding about 1/2 inch from the belly of the airplane, this way all the goo will be vented out, and if you like you can also have a syringe with after run oil lubricate the engine as mentioned above, by using a large silicone tube, there's no restriction to the crankcase when expelling the used up oil. It sures beats the mess 4 strokes create when operating.