PrettyPipes/src/main/resources/assets/prettypipes/blockstates/pipe.json

{
    "multipart": [
        {
            "apply": {
                "model": "prettypipes:block/pipe_center"
            }
        },
        {
            "when": {
                "north": "connected_pipe|connected_inventory"
            },
            "apply": {
                "model": "prettypipes:block/pipe_end"
            }
        },
        {
            "when": {
                "south": "connected_pipe|connected_inventory"
            },
            "apply": {
                "model": "prettypipes:block/pipe_end",
                "y": 180
            }
        },
        {
            "when": {
                "east": "connected_pipe|connected_inventory"
            },
            "apply": {
                "model": "prettypipes:block/pipe_end",
                "y": 90
            }
        },
        {
            "when": {
                "west": "connected_pipe|connected_inventory"
            },
            "apply": {
                "model": "prettypipes:block/pipe_end",
                "y": 270
            }
        },
        {
            "when": {
                "down": "connected_pipe|connected_inventory"
            },
            "apply": {
                "model": "prettypipes:block/pipe_end",
                "x": 90
            }
        },
        {
            "when": {
                "up": "connected_pipe|connected_inventory"
            },
            "apply": {
                "model": "prettypipes:block/pipe_end",
                "x": 270
            }
        }
    ]
}