RTV Silicone Sealant,8 oz Can,Red (27085)

Find yourself a small flat topped plastic cap (copper tubing cap comes to mind) and place over the tip, squeeze just enough silicone out to fill the cap til it starts to ooze out the bottom a bit . Then put the original lid on and this stuff and it lasts for months, maybe years if you use it once in a while. Just be sure to clean the small cap, refill and close with original cap each time.