Neither is good Latin. The first one:
Sumus semper in excretum, sed alta variat
... translates as:
We are always in [excretum], but [alta] changes.
Excretum is the accusative of the supine of excerno 'to separate'; presumably excrementum is meant, but it should at least be in the ablative—excremento. (The English verb excrete does derive from excretum, but that's a late development.) Alta is some form of the adjective altus 'high, deep'; a noun is required, like altitudo, in the nominative as it's the subject of variat. (Latin doesn't distinguish between depth and height; they're two aspects of a single concept to a Roman.)
The corrected sentence is then:
Sumus semper in excremento, sed altitudo variat.
The second sentence:
Semper in excretia, sumus solim profundum variat
... translates as:
Always in [excretia], we are [solim] the depth changes.
Excretia isn't a word at all, and again excremento is meant. The comma is presumably misplaced, with the sumus belonging to the first part of the sentence. Solim is not a word either; it's probably a typo for the adverb solum 'only', possibly with contamination from olim 'then, often' to give it a more adverby feel. Profundum does mean 'depth' but not in the sense intended; it means 'the depth' in the sense of 'the abyss'. Again altitudo is the better choice.
The corrected sentence:
Semper in excremento sumus, solum altitudo variat.
The word order doesn't really mean anything in this case, and the only difference between the two corrected sentences is sed 'but' versus solum 'only'. If you want to match your English sentence closely, go with solum and omit sumus.
Really, though, this may be one of those things where the deliberately bad Latin is considered part of the charm, like "Nolite te bastardes carborundorum" or "Semper ubi sub ubi".