I got sick of my gas can spouts not working properly, slow flow not working at all or spilling. So I replaced the broken/defective spouts on several of my gas cans with EZ-Pour Kits. That I purchased on amazon you can find them here https://amzn.to/2WcvaG1 fur under $12 dollars shipped with prime.
I have purchased 3 of these kits and plan to buy more to do the rest of my larger cans. These may not work well on smaller cans, used for filling chainsaws etc, I think the nozzle may be to large for those purposes. If they make a kit with a smaller nozzle I may try converting those as well when needed.