This topic is one of the most controversial in the maple industry. There are two schools of thought when it comes to cleaning tubing at the end of the season. You attack the woods with air, water and cleaners declaring war on bacteria. Your conscience is tell you, you have to do something. The second school of thought is, even if I go through all of the processes it never turns out the way I want so why bother. Pull the taps and walk away. Trust me, if you have thousands of taps that is usually the game plan.
The primary reason for cleaning lines is to remove the debris and kill the bacteria. Flushing a line with water will remove most of the debris but it will not kill the bacteria and mold forming fungi. Based on studies at the UVM Proctor Research Center and The Cornell University it takes sanitizer to kill bacteria. It is not enough to kill the surface bacteria but you need to kill the bacteria that are locked up in the biofilms that form on the surface of the tubing walls. This requires contact time to accomplish. If your sanitizer is only in contact with the tubing surface for a few seconds, this approach has an affect but only a minimal affect. Studies done by Steve Childs at the Cornell Maple Program clearly show that sanitizers if allowed to come in contact for extended periods are very affective. This research required removing the spouts and drops and allowing them to soak in a sanitizer over an extended period. Again a lot of work and additional expense. A good approach for the hobby producer. Only two chemical cleaners have been proven effective and safe. The first is food grade Hydrogen Peroxide and the other is a bleach solution. The latter being the most effective. The negative side of bleach is the possibility of a salt residue if not flushed with water. This can leave an off flavor and will attract our bushy tailed friends. Hydrogen Peroxide is the most often used alternative. I did not mention Isopropyl Alcohol because its use is illegal in the United States. Do not go there!
In multiple studies at UVM Proctor Research Center the two most popular methods were flushing with air and water and vacuum drying the lines. The Air/H20 system works well for the small and medium size producer. For the large producer pulling spouts under vacuum and allowing the lines to dry out by air movement has become popular. Either one is preferred over doing nothing. 3/16 producers are somewhat limited to what they can do to clean lines. Doing nothing is a recipe for disaster. Due to the small diameter and the absence of high vacuum pumps, 3/16 line are subject to plugging. Some sort of flush with water and air is probably the best choice. There has also be some experimentation with different chemical additives but this is in the early stages of research.
The final thought is what are you going to do prior to next season. Research has shown that reusing old spout and drops in 5/16 or 3/16 systems will lead to poor production. Producers need to use a new spout every season. If you do this along with systematically replacing your drops every 3 years, you should be relatively successful maintaining production. Another practice gaining in popularity is running the vacuum pump continuously throughout the season to keep the lines cool and clean.
After years of attacking the woods with high pressure air and water. That resulted in lines being blown apart and stagnant water in in laterals and drops we have come up with this solution. At the end of the season, we bring the whole woods up to operating vacuum by repairing all of the leaks prior to pulling the taps. Once we are up to normal operating vacuum we close all of the main lines and open each line one at a time. Starting at the back of the mainline on the furthest lateral we cut off the old spout and pull the tap. This results in a sudden gulp of air entering the drop line, expelling any liquid from the line. We then plug the drop line with a drop plug. We use DSD multi fittings to plug the drop. The capping maintains the vacuum in your system and preventing backflows. Do this with every lateral from the anchor to the mainline. At the end of the day, open all of the main lines pulling the garbage toward the releaser. We will then flush out the wet/dry lines and the pump lines with water. Make sure you clean your moisture traps and releasers thoroughly. An alternative to this method is to pull all the taps under vacuum and open the drops to the air. In the fall come back in and flush the lines. Your releaser should be taken back to the shop where you can inspect O-rings and lubricate the mechanism. Next spring you will be ready to put on