I'm not sure where I got this from originally, but I've used it for several years on the acre around my house, and it has generally worked very well, at least for me. You take equal parts of
mouthwash (cheap works as well as name-brand), beer (again, cheap works as well) and Epsom salts. Mix until Epsom salt is dissolved, place in a sprayer and spray close to
the ground and generally around any trees, shrubs, etc. on a dry day. I live next to a small lake, and have dense woods surrounding the property so there are always areas of water
for the mosquitoes to breed in, but I have had very little problem around my house and garden. In 2012 when we had the drought here, I didn't spray at all.
One thing I've also noticed personally is while I used to be very sensitive to mosquito bites, now if I do get bit, I have little or no itching or reaction to the bite. I do not know whether my
system has become less sensitive or the mosquitoes are now less toxic.
Besides brewers yeast, I have also heard zinc is helpful, as it is disruptive to the mosquito's reproductive system.