掃き溜めと金持ちは溜まるほど汚い
(Hakidame to kanemochi wa tamaru hodo kitanai;
“Dunghills and money get dirtier as they accumulate”)

Definition:

The more money someone has, the more money they want; an increase in wealth tends to bring increasing greed and selfishness rather than contentment.

Breakdown:

We begin with the verb 掃く (haku), “to sweep,” in conjunctive form. This connects it to 溜める (tameru), “to accumulate (something).” This verb is also in conjunctive form, but here the form allows it to act as a noun. (One could also argue that haki is acting as a noun as well, making this phrase a compound noun.) Put together, 掃き溜め refers to a heap of trash or manure.

Jumping forward just a bit, we find the noun 金 (kane), “metal,” especially “gold,” or by extension, “money,” compounded with another verb-derived noun; this one from 持つ (motsu), “to have.” A money-haver, of course, is a rich person. This compound noun is joined to the hakidame with exclusive-and particle と (to, pronounced like “toe”), i.e. “this and this (and not particularly any others).” The category of these two things is then marked as the topic of conversation by particle は (wa).

The comment on this topic is the adjective 汚い (kitanai), “dirty,” in conclusive form. This is preceded and modified by noun ほど (hodo), “degree,” “extent,” which links the dirtiness to the verb 溜まる (tamaru), “(something) accumulates,” in prenominal form.

Notes:

A variant saying switches and replaces things a bit, giving 金持ちと灰吹きは～ (kanemochi to haifuki wa…), the dirty things in this case are “rich people and ashtrays.”

Example sentence:

「掃き溜めと金持ちは溜まるほど汚いと言うから、貧乏から抜け出して、単純に生活に困ることのない暮らしができればそれでいいと思ってた。けど、このことわざをよく考えてみると、どんな程度であれ、お金を持てば困ることが増えていくということなんじゃないかと思う」

(“Hakidame to kanemochi wa tamaru hodo kitanai to iu kara, binbou kara nukedashite, tanjun ni seikatsu ni komaru koto no nai kurashi ga dekireba sore de ii to omotteta. Kedo, kono kotowaza wo yoku kangaete miru to, donna teido de are, okane wo moteba komaru koto ga fuete iku to iu koto nan ja nai ka to omou.”)

[“They say that like a trash heap, money only gets dirtier the more you pile on, so I thought that it would be best if you could just get enough to escape from poverty and simply live without any worries. But thinking about the saying, I realize that no matter how much money you have, it only gives you more to worry about.”]