Fascinating subject, no? I'm even going to jazz it up by talking about shampoo as well. And dish detergent. And body wash. Hold onto your seats.
When my kids were younger I used to gasp at the sheer amount of bath products they went through. But kids will be kids, I just sucked it up and went with cheaper stuff for them, and anyway, cheap stuff was all my budget allowed.
When we got to Finland they were suddenly pouring someone else's money down the drain with that body wash (my poor husband's money, that is). In a mini-epiphany I put the kids' body wash into a small pump container.
Literally overnight their consumption of the stuff dropped in half. My husband, confused by the container, used it as well, so we all ended up using less. We then adopted pump packs for the shampoo and conditioner.
Along those lines, while out shopping (and armed with a dictionary to try and understand the labels) I found a place selling 3 litres of hand soap for the same price we'd been paying for one litre. Score! Not only that, but it's actually sold for use as hand soap AND body wash AND shampoo. Turns out that this stuff is a little too squeaky to enjoy as shampoo, but it's fine as body wash, and it comes in five different scents, just for variety. I bought some for the AirBnB let as well, but often guests leave products behind and I in turn leave those for the future guests to use.
As far as shampoo is concerned, we love the sweet-smelling fancy anti-dandruff stuff but prefer the price tag of cheap stuff that smells like air... we compromise by using a mix of half and half in our pump and it works just fine.
Now I also promised to talk dish detergent. No pump pack here, but my kids (again) were squirting it in huge amounts. I melted/squished the nozzle half-closed and now it allows only a little to come out. Another victory in cutting down the amount wasted.
It all comes down to measuring - if you pour it freestyle you end up pouring more than you need. So along those lines, I now always measure my clothes washing detergent and conditioner. Goodness knows how much I used to use when I was just eyeballing it and pouring it in...
What sort of effort does it all take? Well apart from refilling containers once a month, none really. I was about to say that the savings are not enough to buy an apartment with, but actually, it all adds up and is a substantial saving over the course of a year. The more frugal I can be, the earlier we can retire. And I'm very lazy, so the more effortless frugal things that I find... the better. :)