Our sewer line is 43" above the ground. Today, the washing machine drains into a washbasin, into a ejector pump and into the sewer. I'd like the washing machine to drain directly into the sewer line, bypassing the washbasin and pump. Can modern washers pump the water high enough to allow for a trap above the 43"?
No. Well maybe it can, but it shouldn't.
If you check the documentation that came with the washer, it should contain the maximum drain height. Generally, the maximum height is around 39" (99 cm).
Newer washers often have a drain hose permanently attached, which is designed to make drain installation fool proof. The supplied drain hose shows you exactly how high the washer can discharge.
Raise the washer
Depending on the machine, and whether or not you're already using a pedestal. You may be able to raise the whole machine up, to accomplish what you want. The maximum height is not height above sea level, it's height above the bottom of the washer. So if it's possible to do so, raising the machine up a few inches (safely) might be the solution.
If it's a front loading washer; and you're not already using a pedestal, you may be able to purchase (or build) a pedestal to raise the machine up. If not, you may want to think about building a raised floor to raise the whole area up.
Keep it up to code
International Residential Code (IRC) says.
Which means if you connect the drain hose to a standpipe, the standpipe has to be at least 18" above the point at which water will begin to flow from the trap. So your 43" height, could quickly become 61".