I worked briefly with Dr. Mary Weismantel about 15 years ago when I was junior curatorial staff in the Native American art department of a museum that had a large number of Moche erotic pots - she was working on an [article] (http://onlinelibrary.wiley.com/doi/10.1525/aa.2004.106.3.495/pdf) (which looks like it's behind a paywall, unfortunately) about them.
I recall she came to the conclusion that they were likely intended to be wacky, rather then the gravity-filled comment on human sexuality we were treating them as.
Moche ceramics depicting sex are different from sex scenes on ceramics produced by neighboring cultures in a lot of respects. Why this is the case, and what they were intended to communicate, is a matter of debate, so let me preface this by saying that we can't say much about Moche sexuality from these pots.
Moche sex scenes invariably depict heterosexual anal sex or oral sex performed on men by women. Vaginal sex, oral sex performed on women, and homosexual sex are not depicted (or at best, extremely rare - what exactly is happening on some ceramics is a bit hard to figure out!). Larco Hoyle (1965) hypothesized that the pots acted as teaching tools to illustrate non-reproductive sex methods, but most modern scholarship takes a variety of less-literal interpretations. For example, Gero 2004 interpreted them as symbolic expressions of social power and class dominance because the scenes depicted are pleasurable for the male figures, but (arguably) not for the female figures, who are servicing the men. In contrast, Weismantel 2004 hypothesized that the Moche may have had different premises about the biology of conception, and that the transmission of sexual fluids through oral or anal sex may have been viewed as an important part of ensuring fertility and the lineage of the family.
In any case, we can't conclude much about everyday sexual behavior in Moche society from these ceramics. For example, certainly vaginal sex happened despite its absence from the ceramic record, and the anal and oral sex depicted may be more symbolic than a reflection of typical sexual preferences among Moche men and women.