There's a place in Brunswick Melbourne that sells bulk goods to restuarants (and the public) called Bass Foods. They have a good website. We go there about 3 times a year for our OMO amongst other things. Been doing it for about 5 years now. Saved a small fortune. Very happy with the OMO btw.
I just add them as i do each wash... I don't need to add them to my DH's business shirts load because they don't get very dirty... mainly add it to the kids loads that are heavily soiled.
Also the OMO used to come in big buckets ... I store the powder in that so it's moisture proof... important when you need to store it for several months. I make the transfer as soon as I open the bag then chuck it out.
ETA: make sure you buy homebrand vinegar to keep down costs.
I put about 2 tablespoon of vinegar in the softener dispenser part of my top loading machine then add about 1 level tablespoon (sometimes a bit less) of bicarb as the machine is filling up (soon after I add the OMO). You can also buy bicarb soda in bulk quantities which keeps costs down.
This OMO product wouldn't be suitable for toploaders I don't think although I'm not 100% certain. I know that there is a thread about how the vinegar part is more important for front loaders to reduce the smell that is common with that type of machine.
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