If you coat the bottom of the barrel, and the barrel channel of the stock with a good water repelling grease or lube, appropriate to the temperatures where you live and shoot, you should be able to clean the gun with the pins left in the stock and barrel. there are cleaning devices made to screw into your nipple hole, or to clamp to the vent so that you can flush the barrel using rubber tubing from a pail or bottle of water and cleaning compound. ( soap and water ! ) That is the " neat " way to do the cleaning. I found out how to tip the gun to the side in my bathtub, and simply pour water down the barrel and then drive a cleaning rod with a patch on a jag down on the water and force it out the vent or nipple flashchannel into the tub. The tub gets ugly, but it clean up afterwards with a little bleach. I do think the window cleaner idea is a good one, but be careful about using cleaners with Ammonia in them. Use them, but then flush with water to get the ammonia off the steel. It is corrosive. But there is no doubt that these cleaners attack Black Powder agressively, and get it out .
If you live or shoot in one of the southern tier states, where summer temperature can be 90 degrees and above for months on end, look at some of the synthetic silicon based lubes now made in the auto trade for high temperature performance. They work will in keeping water out of the barrel channel and protecting the bottom half of the barrel from any corrosion. They also work pretty well for below freezing temperature, when most oil based lubes will harden up. If you live and shoot in so temperature in between all those extremes, you can use a good water pump grease to protect that barrel. I have a 1007 year old mauser that came with a coating of waterpump grease between the stock and the barrel including under the handguard. The exposed portion of the barrel shows all kinds of wear from hitting tree branches and other things, with almost no original blue showing. Where the grease protect the barrel, you can see the original finish on the barrel!