Isabella knows what she is talking about. Has anyone experienced a problem with trees being too close to their municipal water service? It is essentially the same thing - a closed sealed pipe. The tree has no idea that there is water in the pipe and is not staying up at night trying to figure out how to destroy it. Septic systems are a completely different matter as they are made to leach into the soil. They are opened to the surrounding soil and a water source to whatever is around them. Trees don't search out water, their roots grow more vigorously where they get water and not so much where they don't. It follows that they continue to grow toward the water source. Older septic pipes are also vulnerable because they are fitted together rather than being solid since they run on gravity rather than pressure. Those fittings leak creating a water source and the root growth heads to the source and finally into the leaking joint. A sealed water pipe from a well or municipality is not going to attract root growth.

What I did this year was remove the lowest limbs. I did not do this for the bloom, I just like the look of the multiple trunks. The bark of a Crape is part of the attraction (color and bark naturally exfoliates). I would give the tree some time. I don't know if it's patience, I just have so many gardening interests that any particular tree or shrub might sulk for a few years w.o. me even noticing. Trees and shrubs are not said to be fully established for up to three years after planting! So too, It might be a soil thing. I did feed mine once in the season as it was pushing new growth, otherwise I do nothing special for them. Make sure you clear the weeds over the drop line and do mulch. (Summers here are usually wet enough to eliminate the need for any watering.) Boy oh boy, do the honeybees love their blossoms!

This might have been mentioned. (I didn't read everything.) If you had a groundcover below the trees, there stands a good chance that many leaves would disappear into it as they sift down, and then just convert to "mulch" over time. I don't think it looks good to have shrubs below the trees as it seems everything is competing visually with everything else. It could either be a tree form with groundcover below, or a shrub form that is allowed to cover all the ground space. Whatever plant (tree or shrub) you pick, if it's reasonably narrow, I wouldn't worry about some if it crossing the property line as that's just the way life is with limited space yards. It happens everywhere. The neighbor has the right to cut back to the property line. Also, I wouldn't worry that a plant is labeled necessarily as "tree" or "shrub". For small trees and large shrubs this is a massive "grey area." Many plants can fit either category depending on how you prune them.

btw .. they are shrubs.. rather than trees ... and as such.. the pruning system is a bit different .... with shrubs.. its called rejuvenation pruning .... and it is often done .... its NBD .... done properly ... unfortunately.. it can be improperly done .. and with CMS ... its called CM murder ... the link below is a few vids dealing with both .... perhaps looking at those.. will calm you down a bit ... and reduce your worries ... that first one.. is his hair real .. lol ... two take aways .... think in shrub time.. he's talking a couple years ... and second .... there will be some annual guidance pruning.. to reshape the thing.. over those years ... a good pain of hand shears will be worth the investment.. imo .... ken https://duckduckgo.com/?q=Crepe+Myrtle+rejuvenation+pruning&t=ffcm&iax=videos&ia=videos ps: one other pic me up ... consider if they werent there.. perhaps the car would have plowed into your house ... or done some kind of irreparable damage to something else ...